We are studying the interactions between different transmitter systems in the rat forebrain and the correlation of motor behavior with the function of defined neuronal tracts (such as the nigrotriatal dopamine tract) in terms of rates of transmitter synthesis. We have measured synthesis rates for dopamine, 5-hydroxytryptamine, and norepinephrine in forebrain regions and have developed methods for estimating GABA synthesis rates. We have studied turning produced by unilateral lesions of the median raphe nucleus and demonstrated changes in dopamine synthesis within the striatum which correlate with motor behavior. We have also studied the control of dopamine synthesis in striatal slices and synaptosomes and have shown that feedback inhibition by DOPA or dopamine can not account for changes in synthesis rate produced in vitro by amphetamine and depolarizing drugs.